Saturday, September 27, 2008

Wins And Plus/Minus

Plus/minus is a bit of a controversial stat. Certainly it needs to be treated with care, because of issues such as quality of opposition, team strength, empty net goals, etc. However, there are many hockey fans who would prefer to throw it out entirely for these reasons.

What is interesting to me is that many of these same people will rely heavily on goaltender wins to evaluate a goalie. Wins are determined by goals for and goals against, so goalie wins measures whether there are more goals for or goals against when a goalie is in the game. That is conceptually similar to plus/minus, the only difference being that a goalie really only has an impact on results at one end of the ice, while a player can go both ways.

So why do many hockey fans rely heavily on goaltender wins to evaluate a goalie, which is basically a measure of the goals for and against while a goalie is in the game, and yet completely reject plus/minus, a measure (however imperfect) of the goals for and against while a player is in the game? Doesn't make sense to me.

3 comments:

So why do many hockey fans rely heavily on goaltender wins to evaluate a goalie, which is basically a measure of the goals for and against while a goalie is in the game, and yet completely reject plus/minus, a measure (however imperfect) of the goals for and against while a player is in the game? Doesn't make sense to me.

Me neither. I like both stats, with limitations. As you say, both are subject to team effects, but are still one measure of the performance of the player. A direct measurement of success, in fact.

To completely reject plus/minus is an over-reaction. Nowadays to put it in perspective there are such other measures as TOI, QualComp and QualTeam; GF/GA when a player is both on and off the ice; empty net goals and shorties can be filtered out. On a bad team the player with the worst minus likely isn't then worst player on the team, he just gets the most TOI and the most responsibility. That's just commonsense; the stat isn't the be-all and end-all, it's just one measurement system. As always, context is critical.

now what to you see, basically a few of the same guys again and again, and then randomly a solid forward or defenseman having a great year redden 06, preissing 07, roy 07, schneider 06. nevertheless its always guys who had great years. so this would indicate an association of relevance, and a positive one at that. so to say these stats are overrated is stupid. now im sure you could cherry pick outliers like ilya kovalchuk, or slant this like you do everything else on the site, but there is a reason that wins and +/- are highly valued stats amongst those that know something about the nhl.

An adjustment that can be made to raw +/- stats is to compare +% to -% (% of team's +'s & -'s)... this allows for a more valid assessment of +/-, and can be done for the older seasons where minutes played, QUALCOMP etc etc is not available.

Unadjusted +/- IS overrated. A plus player is not necessarily better than a minus player; a goalie who "wins" the game may be worse than the goalie who "loses" the game.

About Me

I call myself a contrarian because I rely on stats-based analysis over "watching them play", think large sample sizes are more important than "big saves", prefer to rank goalies on save percentage rather than team success, and rate Dominik Hasek as the GOAT. In other words, pretty much the mainstream views of the hockey stats community, but until the far-off day when hockey broadcasters everywhere start talking about ES SV% instead of GAA and wins, I'll have to keep the moniker and my soapbox about the importance of separating a goalie and his team. I am also on Twitter (@tcghockey).